1. Field of the Invention
The present invention relates to an electrophotographic apparatus that can be adapted for a printer, a facsimile machine, or the like.
2. Description of the Related Art
Traditionally, two-component developing methods that use developer consisting of toner and carrier have been widely used in electrophotography, but in recent years, the development of one-component developing methods has been proceeding aiming at reducing the size and cost of image-forming sections. FIG. 11 shows an example of an electrophotographic apparatus employing such a one-component developing method. In FIG. 11, reference numeral 1 designates an organic photoconductor drum, an electrostatic latent image holding member, coated with a layer of phthalocyanine dispersed in a polyester-based binding resin, and reference numeral 2 indicates a two-pole magnet fixed coaxially with the photoconductor 1. Reference numeral 3 is a corona charging unit for applying a charge on the photoconductor 1; 4 is a grid electrode for controlling the charge potential of the photoconductor 1; 5 is a signal light; 6 is a developer reservoir,; 7 is a one-component magnetic toner which is the developer; 8 is an aluminum electrode roller; and 9 is a two-pole magnet fixed coaxially with the electrode roller 8. Further, reference numeral 10 is an AC high-voltage unit for applying a voltage to the electrode roller 8; 11 is a scraper, made of a polyester film, for scraping toner from the electrode roller 8; 12 is a corona transfer unit for separating the toner image from the photoconductor 1 and transferring it onto paper; and 13 is a 38 .mu.m thick sealing member formed from a polyethylene terephthalate film which is disposed, in contacting relationship with the photoconductor 1, on the upstream side of the developer reservoir 6 in the rotating direction of the photoconductor 1.
The operation of the above electrophotographic apparatus will be described below with reference to FIG. 11. The photoconductor 1 is charged to -500 V by means of the corona charging unit 3 and the grid electrode 4. The photoconductor 1 is then exposed to the laser beam 5 to form an electrostatic latent image thereon. Toner 7 is attracted by magnetic force to the surface of the photoconductor 1 as the surface passes the developer reservoir 6. The revolving photoconductor 1 then passes the electrode roller 8. At this time, an AC voltage of 800 V 0-p (zero to peak) (frequency 3 kHz) with a DC voltage of -300 V superimposed thereon is applied to the electrode roller 8 by means of the AC high-voltage unit 10. This causes toner on the photoconductor 1 to be attracted toward the electrode roller 8, leaving only a reversed toner image in the image areas of the photoconductor 1. The toner adhering to the electrode roller 8 revolving in the direction shown by the arrow is scraped by the scraper 11, and returned to the developer reservoir 6 for use for the next image forming process. The toner image thus formed on the photoconductor 1 is transferred onto paper (not shown) by means of the corona transfer unit 12, and then fused to the paper by a fusing unit (not shown).
The one-component developing method employed in such an electrophotographic apparatus is an excellent developing method that can provide high image quality of very high resolution by supplying a sufficient amount of toner to the surface of a latent image. However, since a sufficient amount of developer must be held at all times between the photoconductor and the electrode roller, a seal for preventing developer leakage becomes an important consideration. In the prior art electrophotographic apparatus shown in FIG. 11, to prevent developer leakage a 38 .mu.m thick sheet-like sealing member 13 formed from a polyethylene terephthalate film and contacting the photoconductor was provided on the upstream side of the developer reservoir in the rotating direction of the photoconductor. However, when printing was performed using such an electrophotographic apparatus, there occurred a problem of partial image dropouts in the case of a fine-line image.
To overcome the shortcomings of prior art sealing members for an electrophotographic apparatus, various sealing member arrangements have been provided.